MOFRISON 



Figure 3 represents an interesting form, the bilby. This is 

 a desert representative of the small group of bandicoots (Perame- 

 lidae) which further emphasizes the independence in the day and 

 night "settings" of the "thermostat." The daytime (inactive) T 

 declined steadily through the course of the experiments, but time 

 played no part in the level of the active temperature which stayed 

 steady at 37 . These two states need not differ very much in activity 

 but merely "wakefulness." The T after forced activity in the day- 

 time never reached the natural nighttime level. Similarly, forced 

 activity at night did not raise the T at all. So these are not passive 

 noncommitants of extra heat production, but rather are maintained 

 levels that are set by the animal. 



Figure 4 recasts these data into a 24-hour cycle to bring out 

 this very sharp nocturnal pattern. Like the brown oppossum, the 

 bilby regulates to a different level during day and night (Fig. 5). 

 The bilby has excellent regulation to cold and this may seem contra- 

 dictory since it is a desert species which comes from the Australian 

 "center" where a high T is the rule. But the bilby shows no evap- 



orative cooling and if put in a hot room at 40 C, elevates its T 



o 

 by 4-6 G within an hour and must be removed to avoid heat dea' 



(Robinson and Morrison, 1957). 



By contrast. Figure 6 shows another bandicoot with fair regula- 

 tion to heat, with the T curve crossing the isothermal line to give 

 T lower than the T. Of course, in terms of the slopes, what would 

 be rather poor regulation to cold represents rather good regulation 

 to heat, and yet this animal comes from the coastal regions, which 

 are considerably wetter and cooler than the "center." So it is of 

 interest that a desert animal need not be characterized by the ability 

 to maintain itself under desert conditions, while an animal from a 

 less rigorous environment can do better. The answer, of course, is 

 in the stringent requirements ofdesert life, such that the bilby must 

 always use microclimatic evasion to avoid the expenditure of water. 



The short-nosed bandicoot showed an interesting feature in rela- 

 tion to the topic of seasonal modification discussed by Dr. Hart. 

 These animals always showed good "cold" regulation at night (Fig. 

 6), and in the winter they regulated well during the day or night. 



392 



